This invention relates to the conversion of coal, and similar porous hydrocarbons, into other, more readily usable, hydrocarbon products, specifically oil and gas. More particularly, the present invention relates to an in situ process for such conversion.
There have been numerous efforts in this general field of in situ hydrocarbon conversion, as reflected by the prior art. For example, U.S. Pat. No. 3,316,020 to Bergstrom discloses an in situ oil shale recovery process in which an impervious wall is constructed around a selected retort space, explosives are used to fragment the oil shale, a combustion-supporting fluid (air) is introduced into the space to volatilize the oil shale rubble, and the volatilized oil and gas product is removed, and processed to recover hydrocarbon fuels in liquid and gas states. U.S. Pat. No. 1,269,747 to Rogers discloses a similar process. U.S. Pat. No. 3,566,377 to Ellington discloses an in situ process for retorting oil shale wherein several areas are retorted in series, and the hot flue gases from one area are passed into the next area to preheat the rubble.
The above prior art in situ retorting processes for oil shale have a number of critical deficiencies. These prior art processes are not economical in that they are expensive and result in a low yield of very low B.T.U. gas products, and they are difficult to control. All of the prior art in situ retorting of coal has been commercially unsuccessful, produced a highly variable, very low B.T.U. gas, had low yields, and been difficult, if not impossible, to control, as well as requiring very specific coal seams. As a result, no reliable process of in situ gasification of coal or similar porous hydrocarbons to yield a high B.T.U. gas has been heretofore known.
The in situ retorting of coal and similar hydrocarbons poses an even more difficult problem than with oil shale because the former materials may be porous and have many fracture paths through them making control even more difficult.